Process control of compacted graphite iron production in pouring furnaces

Abstract

A method for continuously providing pretreated molten iron for casting objects which solidify as compacted cast iron, in which inoculating agents are added immediately prior to casting, in exact quantities. In practicing the method, the ability of the fully treated cast iron to crystallize is measured and the result of this measurement is used for feedback control of the supply of inoculating agent, this supply being effected at the last possible stage of the treatment process, so as to optimize the amount of inoculating agent introduced to the system. Since the inoculating a gent will normally include FeSi, it will also fed back and used to increase or reduce the addition of agents for adjusting the carbon and/or silicon contents of the iron as necessary.

We claim: 
     
       1. A method for continuously providing pre-treated molten iron for casting objects which solidify as compacted graphite iron, comprising the steps of: (a) continuously producing a succession of batches of desulfurized molten cast iron, thereby providing a feedstock thereof;   (b) transferring increments of said feedstock of desulfurized molten cast iron one after another to a conditioning furnace and intermittently dispensing desulfurized molten cast iron from said conditioning furnace into a succession of individual casting molds, said transferring being conducted so as to maintain the quantity of desulfurized molten cast iron in said conditioning furnace within predetermined limits, despite said dispensing;   (c) periodically taking a sample of desulfurized molten cast iron from a respective selected one of said individual casting molds into a container and allowing the sample to solidify to cast iron from a state in which the sample and the container are substantially in thermal equilibrium at a temperature above the crystallization temperature of the sample;   (d) while allowing each sample to solidify to cast iron, recording time-dependent temperature changes of the sample and using the resulting recorded changes for establishing structural properties and carbon equivalent of the cast iron;   (e) comparing the structural properties and carbon equivalent established in each practice of step (d), with known structural properties and carbon equivalent equating to acceptable compacted graphic iron; and   (f) upon determining as a result of a practice of step (e) that the established structural properties and/or carbon equivalent of the cast iron from a respective sample deviate from the respective said known structural properties and carbon equivalent by more than given respective predetermined amounts, practicing at least one of: (i) adjusting the carbon equivalent of a batch or increment of said feedstock, by adding at least one of carbon, silicon and steel thereto;   (ii) adding a correspondingly varied amount of at least one graphite shape-modifying agent to said desulfurized molten cast iron, in relation to an amount of graphite shape-modifying agent added to a respective preceding batch or increment and/or in at a preceding incident of addition, by making a corresponding adjustment of addition thereof to at least one of said batch, said increment and said conditioning furnace; and   (iii) adding a correspondingly varied amount of at least one inoculating agent to said conditioning furnace immediately prior to pouring desulfurized molten cast iron therefrom into a respective said individual casting mold in a respective practice of step (b).     
     
     
       2. The method of claim 1, comprising: practicing step (f)(ii) on respective batches of said desulfurized molten cast iron in a reaction vessel; and   transferring said batches from said reaction vessel.   
     
     
       3. The method of claim 1, further comprising: maintaining said conditioning furnace substantially closed except when transferring desulfurized molten cast iron thereto or therefrom and when adding graphite shape-modifying agent or inoculating agent thereto.   
     
     
       4. The method of claim 3, further comprising: providing said conditioning furnace with a protective internal atmosphere of inert gas.   
     
     
       5. The method of claim 3, further comprising: internally pressuring said conditioning furnace.   
     
     
       6. The method of claim 5, further comprising: reducing internal pressurization of said conditioning furnace when adding graphite shape-modifying agents thereto.   
     
     
       7. The method of claim 1, wherein: each respective selected one of said individual casting molds has a gate or sprue system, and, in practicing step (c), each said sample is taken from a respective gate or sprue system.   
     
     
       8. A method for continuously providing pre-treated molten iron for casting objects which solidify as compacted graphite iron, comprising the steps of: (a) continuously producing a succession of batches of desulfurized molten cast iron, thereby providing a feedstock thereof;   (b) transferring increments of said feedstock of desulfurized molten cast iron one after another to a conditioning furnace, intermittently dispensing desulfurized molten cast iron from said conditioning furnace into at least one ladle, and pouring desulfurized molten cast iron from said at least one ladle into a succession of individual casting molds, said transferring being conducted so as to maintain the quantity of desulfurized molten cast iron in said conditioning furnace within predetermined limits, despite said dispensing;   (c) periodically taking a sample of desulfurized molten cast iron from a respective selected one of said individual casting molds into a container and allowing the sample to solidify to cast iron from a state in which the sample and the container are substantially in thermal equilibrium at a temperature above the crystallization temperature of the sample;   (d) while allowing each sample to solidify to cast iron, recording time-dependent temperature changes of the sample and using the resulting recorded changes for establishing structural properties and carbon equivalent of the cast iron;   (e) comparing the structural properties and carbon equivalent established in each practice of step (d), with known structural properties and carbon equivalent equating to acceptable compacted graphic iron; and   (f) upon determining as a result of a practice of step (e) that the established structural properties and/or carbon equivalent of the cast iron from a respective sample deviate from the respective said known structural properties and carbon equivalent by more than given respective predetermined amounts, practicing at least one of: (i) adjusting the carbon equivalent of a batch or increment of said feedstock, by adding at least one of carbon, silicon and steel thereto;   (ii) adding a correspondingly varied amount of at least one graphite shape-modifying agent to said desulfurized molten cast iron, in relation to an amount of graphite shape-modifying agent added to a respective preceding ladle of said feedstock, by making a corresponding adjustment of addition thereof to a respective said ladle; and   (iii) adding a correspondingly varied amount of at least one inoculating agent to a respective said ladle prior to pouring desulfurized molten cast iron therefrom into a respective said individual casting mold in a respective practice of step (b).     
     
     
       9. The method of claim 8, further comprising: maintaining said conditioning furnace substantially closed except when transferring desulfurized molten cast iron thereto or therefrom and when adding graphite shape-modifying agent or inoculating agent thereto.   
     
     
       10. The method of claim 9, further comprising: providing said conditioning furnace with a protective internal atmosphere of inert gas.   
     
     
       11. The method of claim 9, further comprising: internally pressurizing said conditioning furnace.   
     
     
       12. The method of claim 8, wherein: each respective selected one of said individual casting molds has a gate or sprue system, and, in practicing step (c), each said sample is taken from a respective gate or sprue system.